The measurement of marker gases in human exhaled air represents a future noninvasive technique for detecting diseases and metabolic disorders. Possible applications in this case relate to screening, differential diagnosis as well as therapy optimization. Examples of this are NO detection for progress monitoring of an asthma therapy or differential diagnosis of COPD, the detection of lung tumors, TB or lung inflammation.
EP 1 384 069 discloses a breath conversion module to which the respiratory gas is delivered, before it is sent to the actual sensor unit. The purposes of this breath conversion module are, for example, to dehumidify the breath in order to avoid excessive loading of the sensor unit with moisture, as well as conversion of particular breath components. In the case of the asthma application, for example, NO is oxidized to NO2. This is an example of the converter function in which an analyte gas, which can be detected only with difficulty, is converted into another gas which can be readily measured by the sensor. In other cases, interfering gases are oxidized to gases which cannot be detected by the sensor.
These converters wear out, and their lifetime is limited. It is possible to carry out replacement of the filter or converter after an estimated lifetime or number of use cycles. This method, however, is susceptible to error since exact monitoring of the intensity of use is necessary. Other errors are also possible: in order to avoid ageing during storage, the filter or converter is isolated from the ambient air by packaging before use or by valve control in the apparatus. If this is not achieved, the risk of premature ageing and false measurements of the breath analyzer arises.